In order to solve a price increase of crude oil and natural gas and a global warming problem caused by the use of fossil fuel, an effort for deviating from dependence on the existing fossil fuel has recently been actively conducted. However, the fossil fuel is occupying a substantial portion of energy consumed all over the world up to now, and an energy consumption structure in which the fossil fuel is mainly used is expected to continue for the present.
Coal has a reserve life of two hundred years or more, which is longest among those of current fossil fuels, has a relatively cheap cost per heat amount, and may be mined at various regions. Due to the above-mentioned advantages, research into various methods of obtaining natural gas from the coal has been conducted.
The natural gas obtained from the coal has been called methane or substitute natural gas (hereinafter, referred to as synthetic natural gas) and has been expressed as synthetic or substitute natural gas (SNG). As a method of obtaining the SNG from the coal, there are a method of obtaining the SNG through a methane synthetic reaction using synthetic gas obtained through gasification of the coal as a catalyst (a gasification method), a method of obtaining the SNG by allowing the coal to react directly to hydrogen (a hydrogasification method), and a method of obtaining the SNG by allowing the coal to react to vapor at a low temperature using a catalyst (a catalytic gasification method). The method of producing the SNG based on the gasification in which the SNG is synthesized from the synthetic gas (having CO and H2 as main components) obtained by performing gasification of the coal (CO+3H2→CH4+H2O) is classified into an indirect method, and the hydrogasification method in which the SNG is obtained by allowing carbon within the coal to directly react to hydrogen supplied from the outside (C+2H2→CH4) and the catalytic gasification method in which the SGN is obtained by allowing carbon within the coal to react to vapor (2C+2H2O→CH4+CO2) are classified into a direct method.
Describing the method of producing the SNG from the synthetic gas obtained through the gasification of the coal (the indirect method) among the above-mentioned methods, a process of producing the SNG from the coal is mainly divided into a synthetic gas producing process (a process of producing the synthetic gas having CO and H2 as the main components from the coal) and a process of synthesizing the SNG using a catalyst (a process of synthesizing the SNG from the synthetic gas having CO and H2 as the main components), wherein the synthetic gas producing process is configured to be significantly similar to a gasification process and a synthetic gas purification process in an integrated gasification combined cycle (IGCC) process. However, since a ratio of H2 to CO within the synthetic gas discharged during gasification of the coal is 1.0 or less, a water gas conversion process (CO+H2O→H2+CO2) of increasing a concentration so that the ratio of H2 to CO becomes about 3.0 is required, and a purification process having a higher degree than that of the purification process in the existing IGCC due to characteristics of the SNG requiring a H2S concentration at a ppb level within the synthetic gas is required.
Meanwhile, the synthetic gas subjected to the water gas conversion process and the synthetic gas purification process may be converted into methane under a catalyst having Ni supported on a ceramic support as a main component. Since the methanation reaction (3H2+CO→CH4+H2O) is a very strong exothermic reaction (having reaction heat of 206.1 kJ/mol), in the case of using the catalyst produced using the ceramic support having low thermal conductivity, catalyst activity is deteriorated due to sintering, or the like, caused by an increase in catalyst temperature. Design of a methanation reactor capable of easily performing heat control may be the most important core technology.
As a method used in order to prevent a rapid increase in temperature in this reaction process, methods such as a gas recycling method of recycling a portion of reduced gas toward an introduction side of a methanation reactor, a gas distributing method of distributing synthetic gas introduced into a methanation reactor, and a reactor serial connection method of preventing an increase in temperature due to a rapid reaction in a single reactor by sequentially connecting several reactors in series with each other, or the like, have been attempted. However, in a reactor design technology for efficiently controlling reaction heat in a methanation reaction, continuous improvement or introduction of a new technology has been demanded even up to now.